Many manufacturing processes include the fixing of the article to be worked on (i.e. the workpiece) in a chuck, workhead or the like and the subsequent rotation of that chuck or workhead, and the workpiece carried thereby about a predetermined axis of rotation that quite often extends through the workpiece. The workpiece may be a piece of raw stock or it may be a partially manufactured item or assembly of parts. In many instances the machining or manufacturing process requires the accurate locating and positioning of the workpiece in the chuck or workhead and with respect to the worktool or other reference carried by the machine tool.
Rough positioning of a part to be machined or otherwise subjected to a manufacturing process is sometimes accomplished by a feeler or probe that senses a locating characteristic or object carried by the workpiece. Such characteristic or object may be a hole, dimple, groove, rib or similar and intended locating mark provided on the workpiece. However, rough positioning, especially in a radial sense, may be insufficient to locate and position some workpieces for particular manufacturing operations; especially those that require an accurate machining of the peripheral configuration of the part or parts such as that of a cam or cams on a cam shaft.